This ruby gem provides methods that return the raw XML/Atom file from http://gdata.youtube.com along with wrappers to make it's use simpler. It was developed for gtk2youtubeapp, version 2. You'll want to read google's developers guide.
...and this is not a Ruby Gnome app either.
Provides youtuber-dl, to download videos (as of 1.5, should now work on Windows).
- youtuber-dl fmt filename videoid